The present invention relates generally to integrated circuits and, more particularly, relates to integrated circuits having a mechanically robust bond pad.
Integrated circuits are formed on semiconductor substrates using a number of different processing operations that create the circuit elements. In order to access circuitry associated with the semiconductor substrate, bond pads are formed on the integrated circuits. Bond pads provide the means for transfer of electrical signals and power from and to the semiconductor substrate via probes, bonding wires, conductive bumps, etc.
Bond pads are typically formed of aluminum because aluminum is self-passivating and, therefore, more resistant to degradation from atmospheric pressure. Aluminum, and more recently, copper are used for the metal layers within the integrated circuit. Copper is more preferred because of its improved electromigration performance and ability to support higher current density as compared to aluminum.
In order to realize the advantages of the self-passivating character of aluminum and the superior electrical characteristics of copper, composite bond pad structures can be used in integrated circuit designs. In composite bond pad structures, copper is used for the underlying layer of the pad that interfaces with other layers in the integrated circuit. A corrosion-resistant aluminum capping layer is formed on top of the copper portion that creates an hermetic seal that protects the copper portion from atmospheric exposure. In order to physically separate the copper and aluminum portions of the composite bond pad while allowing for electrical connectivity, a relatively thin barrier metal layer may be formed at the interface.
Problems can arise in composite bond pad structures when test and probe operations are performed. To achieve good electrical continuity with the bond pad, elements such as probes must exert forces that can damage or displace portions of the bond pad surface. In addition, if the probe exposes the underlying copper to the ambient, degradation of the copper can occur.
Another problem that can arise with bond pad structures concerns the physical force exerted on the bond pad by a probe that can propagate to lower layers based on the physical couplings within the integrated circuit. Low Young's modulus dielectrics underlying the bond pad may not be able to support such stress resulting from the force propagation.
Various solutions have been proposed for improving bond pad integrity.
Pozder et al. U.S. Patent Application Publication US 2001/0051426, the disclosure of which is incorporated by reference herein, discloses in FIG. 2 a composite bond pad comprising copper (but alternatively could comprise aluminum), dielectric support structures and then a final layer of aluminum. The dielectric support structures can have different configurations as shown in FIG. 5 of the reference. These support structures provide mechanical shielding of the interface formed between the aluminum layer and the underlying copper layer.
Ma et al. U.S. Patent Application Publication US 2002/0068385, the disclosure of which is incorporated by reference herein, discloses an anchored bond pad in which a bond pad is formed on a dielectric layer wherein the dielectric layer has via openings which are filled with metal. The metal-filled via openings secure the bond pad to the dielectric layer.
Ming-Tsung et al. U.S. Pat. No. 5,703,408, the disclosure of which is incorporated by reference herein, discloses a bond pad structure in which stripes are formed in a sublayer which induce an irregular surface of the top metallic bond pad. An object of this particular arrangement is to increase the adhesion of the various layers that make up the bonding pad. Similarly, Mukogawa Japanese Published Patent Application JP 3-96236, the disclosure of which is incorporated by reference herein, discloses an irregular sublayer which induces an irregular surface of the top layer.
Saran et al. U.S. Pat. No. 6,143,396, Saran U.S. Pat. No. 6,232,662, Zhao U.S. Pat. No. 6,198,170, and Saran et al. U.S. Pat. No. 6,448,650, the disclosures of which are incorporated by reference herein, all disclose various reinforcing schemes under the bonding pad. Thus, in Saran et al. U.S. Pat. No. 6,143,396, a metal bond pad is supported by a layer of dielectric and a reinforcing structure. In Saran U.S. Pat. No. 6,232,662, a metal bond layer is supported by an interlevel dielectric layer and a reinforcing layer comprising metal and reinforcing dummy structures. In Zhao U.S. Pat. No. 6,198,170, a bonding pad is supported by a large via and several layers of alternating segments of metal and dielectric. Lastly, in Saran et al. U.S. Pat. No. 6,448,650, a metal bonding pad is supported by a first dielectric, then an interlevel dielectric and finally by a reinforcing layer comprising alternating dielectric and metal.
A need exists for an improved bond pad that can survive forces applied by probing and packaging and which will protect the underlying metal layer, preferably which is copper.
Accordingly, it is an object of the present invention to have an improved bond pad which is mechanically robust to survive the forces of probing and packaging.
It is another object of the present invention to have an improved bond pad which can survive probing and packaging and which can also protect the underlying metal layer.
These and other objects of the present invention will become more apparent after referring to the following description of the invention considered in conjunction with the accompanying drawings.